Interplay of Noncovalent Interactions in Ribbon-like Guanosine Self-Assembly: An NMR Crystallography Study

摘要

An NMR crystallography study shows how intermolecular N-H center dot center dot center dot O, N-H center dot center dot center dot N, O-H center dot center dot center dot N, O-H center dot center dot center dot O, and CH-pi interactions stabilize the ribbon-like supramolecular structures of three different guanosine derivatives: guanosine dihydrate (G), 3',5'-O-dipropanolyl deoxyguanosine (dG(C-3)(2)), and 3',5'-O-isopropylideneguanosine hemihydrate (Gace). Experimental solid-state H-1 NMR spectra obtained at 20 T using fast magic-angle spinning (MAS), here at 75 kHz, are presented for a dihydrate of G. For each guanosine derivative, the role of specific interactions is probed by means of NMR chemical shifts calculated using the density functional theory (DFT) gauge-including projector-augmented wave (GIPAW) approach for the full crystal and extracted isolated single molecules. Specifically, the isolated molecule to full crystal transformations result in net changes in the GIPAW calculated 1H NMR chemical shifts of up to 8 ppm for O-H center dot center dot center dot O, up to 6.5 ppm for N-H center dot center dot center dot N and up to 4.6 ppm for N-H center dot center dot center dot O hydrogen bonds; notably, the presence of water molecules in G and Gace reinforces the molecular stacking through strong O-H center dot center dot center dot O hydrogen bonds. The sugar conformations are markedly different in G, dG(C-3)(2), and Gace, and it is shown that the experimental C-13 solid-state NMR chemical shift at the C8 position is a reliable indicator of a "syn" (>135 ppm) or "anti" (<135 ppm) conformer.